There are many ways and tools to use proxy in Linux. But, let's use what I already used.

GUI

This is the easiest way. If you have a GUI settings, just search for Network > Network Proxy > Manual.
Fill in the input with your own proxy settings.

Manual with CLI

System-wide

Create or add the following line into /etc/profile.d/proxy.sh:

# for all users
export http_proxy="http://<hostname>:<port>"
export https_proxy="http://<hostname>:<port>"
export ftp_proxy="http://<hostname>:<port>"
export no_proxy="127.0.0.1,localhost,::1"

# for curl
export HTTP_PROXY="http://<hostname>:<port>"
export HTTPS_PROXY="hhttp://<hostname>:<port>"
export FTP_PROXY="http://<hostname>:<port>"
export NO_PROXY="127.0.0.1,localhost,::1"

Make it executable:
```
sudo chmod +x  /etc/profile.d/proxy.sh
```
Start using proxy by source it or simply re-login:
```
source /etc/profile.d/proxy.sh
```
Confirm:
```
env | grep -i proxy
```
Remember! If your proxy need authentication just add <username>:<password> before <hostname> and use @ as separator.
```
http://<username>:<password>@<hostname>:<port>
```

Environment Variables

Environment variable is a system variable. But, instead of being part of a program, its part of your terminal. So the proxy you set can only be used in that terminal and if you close the terminal all settings will be lost.

Run the following command depending on your need:

Set HTTP proxy

export http_proxy=http://<username>:<password>@<hostname>:<port>

Set HTTPS proxy

export https_proxy=http://<username>:<password>@<hostname>:<port>

Set FTP proxy

export ftp_proxy=http://<username>:<password>@<hostname>:<port>

or if you want all protocols using the same proxy, run:

export all_proxy=http://<username>:<password>@<hostname>:<port>

Remove this <username>:<password>@ if your proxy doesn't need authentication.

Back to the previous problem, how do we keep our proxy settings? Here bashrc file comes!

Create or add the following line into ~/.bashrc, depending on your need:

export http_proxy=http://<username>:<password>@<hostname>:<port>
export https_proxy=http://<username>:<password>@<hostname>:<port>
export ftp_proxy=http://<username>:<password>@<hostname>:<port>
export all_proxy=http://<username>:<password>@<hostname>:<port>

Run source to execute ~/.bashrc or simply close and open your terminal again:
```
source ~/.bashrc
```
Let's check our settings:
```
env | grep proxy
```

Now check if our proxy works or not:

wget www.example.com && curl www.example.com

Keep in mind that bashrc method only works for a particular user. So if you run a command using sudo, it does not work. To make it work, you have to use the -E option of sudo. Check out the man page of sudo to learn more about the -E option.

sudo -E your_command

Package Managers

pacman

If you're on XFCE environment, uncomment the following line in /etc/pacman.conf:
```
#XferCommand = /usr/bin/wget --passive-ftp -c -O %o %u
```

We know that root is the only user that can run pacman. By simply changing environment variables, we can use proxy on pacman. Run the following commands depending on your need:

export http_proxy=http://<username>:<password>@<hostname>:<port>
export https_proxy=http://<username>:<password>@<hostname>:<port>
export ftp_proxy=http://<username>:<password>@<hostname>:<port>
export all_proxy=http://<username>:<password>@<hostname>:<port>

then use -E option on sudo:

sudo -E pacman ...

More information: https://wiki.archlinux.org/title/Proxy_server

apt

Create or add the following line in /etc/apt/apt.conf.d/80proxy:

Acquire::http::proxy "http://<username>:<password>@<hostname>:<port>";
Acquire::https::proxy "http://<username>:<password>@<hostname>:<port>";
Acquire::ftp::proxy "http://<username>:<password>@<hostname>:<port>";

wget only

[Arch Linux]

Uncomment the following line in /etc/wgetrc:

https_proxy = http://<hostname>:<port>
http_proxy = http://<hostname>:<port>
ftp_proxy = http://<hostname>:<port>
use_proxy = on

[Ubuntu]

Create or add the following line into ~/.wgetrc:

use_proxy = on
http_proxy = http://<hostname>:<port>
https_proxy = http://<hostname>:<port>
ftp_proxy = http://<hostname>:<port>

Web Browser

Go to Settings > Network Settings (The location of the network settings in the browser is different, so just look for it or find it in the search bar with keyword "proxy").

Notes

Some particular application use UPPER CASE version of proxy rules. It's recommended to add it along with lower case. i.e:

http_proxy=http://<hostname>:<port>
HTTP_PROXY=http://<hostname>:<port>
ftp_proxy=http://<hostname>:<port>
FTP_PROXY=http://<hostname>:<port>
all_proxy=http://<hostname>:<port>
ALL_PROXY=http://<hostname>:<port>
https_proxy=http://<hostname>:<port>
HTTPS_PROXY=http://<hostname>:<port>

If you want bypass proxy on certain IP, use:

no_proxy=localhost,www.example.com,127.0.0.1,::1
NO_PROXY=localhost,www.example.com,127.0.0.1,::1

kiraio-moe/proxy-in-linux.md

GUI